The objectives of this project are to grow virulent Treponema pallidum, in vitro and to induce immunity to T. pallidum in rabbits. During the past year, research was conducted in four areas. (1) methods were developed for the more optimal growth of Treponema hyodysenteriae. The basal medium is trypticase soy broth (TSB) which may be prepared anaerobically by three methods (each method results in a slightly different oxidation-reduction potential). The TSB is supplemented with 10% fetal calf serum (FCS) and the organism is inoculated into the medium under an atmosphere of 50:50 H2 and CO2. (2) Attempts were made to grow virulent T. pallidum (Nichol's strain) under similar conditions as those developed for growth of T. hyodysenteriae. (3) Treponema hyodysenteriae was discovered to be capable of O2-uptake. The O2-uptake by both T. pallidum and T. pallidum and T-hyodysenteriae was slightly inhibited by sodium cyanide and markedly by potassium thiocyanate. These results indicate that the mode of O2-uptake may be similar for the two organisms. (4) Attempts were made to immunize rabbits with antigens prepared from T. hyodysenteriae for the prevention of T. pallidum infection. Female rabbits which were immunized during a period of 12 weeks developed less severe skin lesions as compared to non-immunized control rabbits.